In general, a discharge lamp is a light source that uses a discharge phenomenon generated in gas or vapor. Discharge in the discharge lamp may be arc discharge or glow discharge, or may be a discharge which a fluorescent material is applied in a tube of a low pressure mercury lamp. The discharge lamp comprises a carbon-arc lamp, a sodium lamp and a mercury arc lamp which use the arc discharge, and comprises a neon sign which uses a luminescence generated by the glow discharge, and the like.
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. The fluorescent lamp is connected with a ballast in serial for preventing from increasing of current, where the ballast is a choke coil that coils are wound around an iron core. Besides, light in the fluorescent lamp is emitted by a discharge in a low pressure mercury vapor. As a general characteristic of the discharge lamp, since the voltage required for the discharge goes down when electric current flows, a predetermined voltage must be applied to generate the discharge. When the electric current increases excessively, the lamp may be breakdown. Accordingly, a ballast is connected with the lamp in serial to prevent from increasing of current. In principle, a metal resistor instead of the ballast may be used, but since the heat is generated by the current, a choke coil with a small generation of heat is used. In order to construct a lighting apparatus, the ballast is connected with a fluorescent lamp in serial, and both ends of the lamp are connected with a switch or a glow switch in parallel.
An optic output of a usual fluorescent lamp of a bulb type is seriously affected by a temperature of the lamp. For example, when a temperature of the lamp is 40° C., the optic output is maximized. When a temperature of the lamp is a low temperature, a lighting of the lamp turns off and the optic output is declined obviously. Also, when a temperature of the lamp is a high temperature, for example, over 70° C., the optic output is declined. Above all, when a temperature of the lamp is over 100° C., a saturation state occurs due to increase of a mercury vapor pressure sealed in the inside of the lamp, and accordingly, the optic output of the lamp is declined over 30%, and the durability of the lamp is declined obviously.
In addition, the heat generated in the lamp as a lighting apparatus of the discharge lamp is applied to an electronic ballast. Since a durability of the electronic ballast becomes different with a temperature, the fault of the electronic ballast may increase when the temperature rises.
On the other hand, as a high intensity discharge lamp in which the electronic ballast is embedded, a discharge lamp within 30˜100 W to 105˜210 W is mostly used. But, due to a self-heat generation of the high intensity discharge lamp, a durability of the electronic ballast may reduce and an improper lighting of the discharge lamp may occur frequently. Above all, the discharge lamp over 100 W is mostly out of use now due to the heat generated in the lamp.
Besides, when an internal temperature of the electronic ballast is over 85° C., electronic components embedded in the electronic ballast begins to a burning damage, and when an internal temperature of the electronic ballast is over 100° C., the electronic ballast is impossible to use as a lighting apparatus.